1. Field of the Invention
The present invention relates to a constant speed cruise control system of the duty ratio control type and a leading angle control method, and more particularly to an arrangement for performing a control to decrease the car speed deviation quickly and a control to nullify the car speed deviation slowly at the same time, by setting an integrating element 1 responding quickly to a duty ratio change and an integrating element 2 responding slowly to a duty ratio change, in order to reduce the difference between a set car speed and an actual car speed (referred to as a car speed deviation .DELTA.V hereinafter) to zero.
2. Description of the Prior Art
An automotive constant speed cruise control system, known as an Auto-Drive or an automatic speed control, is intended to control the car speed constantly, once a desired car speed is preset, without having to step on the accelerator pedal, and in a generally known system, the coil for a control valve of a negative pressure type actuator used to drive the accelerator link, using an engine negative pressure (e.g. an intake manifold negative pressure, a vacuum pump negative pressure or the like) as a driving source, is driven by a pulse signal of a duty ratio corresponding to the difference between the detected traveling car speed (detected car speed) and the car speed preset by the driver (target car speed).
The constant speed cruise control system of the duty ratio control type controls constant speed travel by determining a set duty ratio which is a duty ratio necessary for traveling at a constant speed at a target car speed (preset car speed), and providing a new ratio by adding or subtracting a duty ratio corresponding to the difference between the target car speed and traveling car speed to or from the set duty ratio. However, the required duty ratio varies with the characteristics of the actuator, throttle drive system or engine, road surface gradient, engine load of air conditioner, vehicle load of speed change gear or other conditions, and if the set duty ratio is fixed, there occurs a car speed deviation corresponding to the difference from the required duty ratio.
In one of the conventional examples of such a constant speed cruise control system, the controller or ECU (electronic control unit) detects the traveling car speed by the signal from a car speed sensor having a reed switch which is turned on and off by a magnet rotating in proportion to the rotation of the vehicle drive shaft. When the present switch is turned on, the ECU stores the traveling car speed, and after it is turned off, it controls the duty ratio of the control valve of the actuator ACT. A negative pressure is introduced when the control valve is turned on, which raises the pressure generated by the diaphragm linked to the throttle valve S1. When turned off, the atmosphere is introduced to lower the pressure generated by the diaphragm. During this control period, the release valve is turned on, and the atmosphere is cut off. When a cancellation signal (e.g. from a clutch switch; or in an A/T car, from a neutral start switch, parking switch, or brake switch) is received, both the control valve and the release valve are turned off, and the atmosphere is let in from both to stop the control swiftly. When a resume switch is turned on after cancellation, control is restored at the car speed stored previously.
A microcomputer is used in the ECU, of which processing is described below. The output duty ratio D for on/off control of the control valve is determined depending on the difference between the target car speed VM stored in the memory and the traveling car speed Vn, but a skip car speed VS adding a car speed variation component (differentiation component) which is used. This is for compensating in advance for the action delay of the actuator, or the loss time due to hysteresis or play of the throttle valve or drive system in a leading direction. Therefore, the skip car speed VS is determined by the following equation. EQU VS=Vn+K x (Vn-V.sub.n-1) (1)
where
Vn: present car speed PA1 V.sub.n-1 : previous car speed PA1 K: proportional constant PA1 VM: target car speed (stored car speed) PA1 VB: control speed width PA1 car speed detecting means for generating a signal in accordance with an actual traveling speed form a car speed sensor; PA1 memory means for storing the actual traveling speed detected by the car speed detecting means as the stored target speed in response to manipulating of a set switch; PA1 means for calculating a set duty ratio SD in accordance with a difference between the actual traveling speed and the stored target speed; PA1 means for actuating the control valve in response to a output duty ratio D which is introduced by adding the set duty ratio SD to the duty ratio; PA1 correction means for amending the set duty ratio SD to exclude a car speed deviation which occurs when the output duty ratio D changes, comprising; PA1 first means for calculating a low-speed integrating element SD1 following gradually to a value of the output duty ratio D in response to changing of the output duty ratio D; PA1 second means for calculating a high-speed integrating element DM following quickly to a value of the output duty ratio D in response to changing of the output duty ratio D; PA1 third means for calculating a first correction value of (DM - SD1)/n PA1 wherein PA1 fourth means for calculating the set duty ratio SD based on the low-speed integrating element SD1 and the first correction value. PA1 (D - DM)/K PA1 wherein PA1 an upper limit and a lower limit are provided in at least one of the low-speed integrating element SD1, the high-speed integrating element DM and the set duty ratio SD. PA1 means for measuring a time Ti of a specified number of consecution the pulses in response to the pulses corresponding to a car speed; PA1 first filtering means for filtering the time Ti; PA1 means for sampling a measuring the time Ti* filtered at a specified time internal and calculating a car speed Sn based on the time Ti* sampled; PA1 second filtering means for outputting as an actual car speed Xn* a value obtained by filtering the car speed Xn. PA1 car speed detecting means for generating a signal in accordance with a actual traveling speed from a car speed sensor; PA1 memory means for storing the actual travelling speed detected by the car speed detecting means as the stored target speed in response to manipulating of a set switch; PA1 means for calculating set duty ratio SD in accordance with a basic duty in a constant speed control; PA1 means for calculating a duty ratio in accordance with a difference between the actual traveling speed and the stored target speed; PA1 means for actuating the control valve in response to a output duty ratio D which is introduced by adding the set duty ratio SD to the duty ratio; PA1 correction means for amending the set duty ratio SD to exclude a car speed deviation which occurs when the output duty ratio D changes, comprising: PA1 first means for calculating a correction value in response to a difference between the set duty ratio SD and the output duty ratio D; PA1 second means for amending the set duty ratio SD in response to the correction value .gamma.. PA1 Thus, in the constant speed cruise control system of duty ratio control type of this invention, since the basic duty ratio value is integrated and corrected by varying the speed depending on the difference from the output duty ratio, the car speed deviation can be eliminated at a practically sufficient speed without sacrificing the stability. PA1 In a preferred embodiment, an upper limit and a lower limit are provided in the set duty ratio SD. PA1 In a preferred embodiment, the first means fixes the correction value .gamma. into values differentiated from one another in car speed regions for a specified speed after setting the target car speed. PA1 In a preferred embodiment, the second means amends the set duty ratio SD as the ratio rapidly changes when a car acceleration exceeds a predetermined limit. PA1 car speed detecting means for generating a signal in accordance with a actual traveling speed from a car speed sensor; PA1 memory means for storing the actual traveling speed detected by the car speed detecting means as the stored target speed in response to manipulating of a set switch; PA1 means for calculating a set duty ratio SD in accordance with basic duty in a constant speed control; PA1 means for calculating a duty ratio in accordance with a difference between the actual traveling speed and the stored target speed; PA1 means for actuating the control valve in response to a output duty ratio D which is introduced by adding the set duty ratio SD to the duty ratio; PA1 acceleration detecting means for detecting an acceleration of a car; PA1 correction means for adding a correction duty ratio to the output duty ratio D when the acceleration exceeds a specified value.
Incidentally, the output duty ratio D may be also determined as follows. ##EQU1## where SD: set duty ratio
In the above equation, VM-VS is a car speed deviation .DELTA.V, and the control speed width VB is an inverse of control gain (i.e. the gradient of the line) G, so that equation (2) may be rewritten as follows. EQU D=G.times..DELTA.V+SD (3)
In the prior art, meanwhile, since the reference value of the duty ratio necessary for constant speed travel is fixed as a set duty ration, a car speed deviation occurs due to fluctuations in the actuator system or vehicle load variations. For example, a shown in FIG. 1, if the set duty ration SD corresponding to the stored car speed VM (e.g. 80 km/h) is 40% and the required duty ratio D is 55%, the control reference point initially located at point A converges at point B along with the decline of the car speed due to the lack of duty ratio. Since the required duty ratio at point B is also nearly 55% (to be more precise, there is a car speed coefficient of about 0.1%/km/h for the required duty ratio as indicated by chain-line 28, but it may be almost ignored in this example), when the control speed width VB is, for example, 20 km/h, a deviation of ##EQU2## occurs, and the car is controlled at 77 km/h at point B.
Accordingly, such a vehicle cruises at a constant speed as shown in FIG. 2, with the travel speeds varying with the road loads.
This phenomenon will be described in further detail.
The prior control system of the constant speed cruise control can be roughly represent as shown in FIG. 3 if its non-linear element is disregarded.
FIG. 4 depicts the control system in terms of its relationships with the target car speed.
Suppose cruising is maintained with an actual car speed in complete agreement with the target value under a particular condition, and that the target speed varies stepwise by a factor of B. Another way of saying this is that to the target car speed V(S) is given B/S, and the target value X(S) transmitted to the feedback system tracks the variation path and converges into V(S) as depicted in FIG. 5. On the contrary, the actual car speed Y(S) varies as in FIG. 5. The final value of the deviation Z(S) between X(S) and Y(S) is given by: ##EQU3##
This indicates that under a given condition there is only one actual car speed, if any which is in perfect agreement with the target value, and that under different conditions a deviation unavoidably occurs between them.
FIG. 6 shows the control system in terms of its relationships with road loads.
Here again, let us assume that cruising is continued with the target car speed and the actual value being in complete harmony with each other. Also assume that load changes occur stepwise by C at time t1.
Expressed in other terms, a load U(S) is given at C/S. F(S) (the car speed corresponding to the load variation) signalled to the feedback system traces the path illustrated in FIG. 7, and Y(S) varies therewith.
This indicates variation in the load induces changes in the actual car speed without any change of the target value, i.e., the actual car speed varies with changing road gradient without varying the target car speed.
If A is made larger to give a smaller deviation regardless of stability, it becomes possible to decrease q(t)t.fwdarw..infin..
This leads to an inevitable reduction of q(t)t.fwdarw..infin. and hence a smaller deviation due to changes in target car speed can be attained, but the variations in car speed due to load changes become greater.
As noted previously, the fixed set duty ration system of the prior art inevitably was involved in the creation of car speed deviations.
Such car speed deviations may be reduced to zero when the control criterion is corrected form point A to point C in FIG. 1. However, if the corrected speed is too low, then deviation convergence takes much time, while if the corrected speed is too high, stability could be impaired due to excessive correction.
Incidentally, since constant speed travel control starts by pressing a set switch while traveling to store the traveling speed at that time as a target car speed, sudden duty ration fluctuations occur right after this setting. Accordingly, i the same control as in the subsequent constant speed travel is effected, the change of SD is too fast, and a car speed hunting as shown in FIGS. 8(A) and 8(B) may continue.
In equation (2), meanwhile, the control speed width VB denotes a range of car speed for varying the output duty ration D linearly in a range of 0 to 100%, and its inverse is the gain. The set duty ratio SD is the duty ratio corresponding to the target car speed VM, and ideally it is the control reference point.
The leading angle control described above obtains a skip car speed (leading angle car speed) VS by adding the differential value (acceleration) V of the traveling car speed Vn, wherein if Vn changes, VS varies as shown in FIG. 9, so that the change in Vn may be fed back to the output duty ratio D in advance.
However, if the car speed changes suddenly due to abrupt variations of the road surface or shift-down of an automatic transmission car, a sufficient controllability (response) is hard to obtain, partly because of the effects of the car speed filter (integrating filter).
Accordingly, one of the objects of the invention is to nullify car speed deviation during constant speed travel.
Another object of the invention is to enhance traveling stability.
A further object of the invention is to prevent hunting right after setting.
Another object of the invention is to make a car speed change small even if a sudden change of a car speed occurs when a road gradient changes suddenly.